This invention relates to novel polymeric material which is capable of mordanting anionic compounds and in particular dyes. This invention relates also to material and in particular to photographic material which comprises a layer having present therein a combination of an anionic compound mordanted by the novel polymeric material.
It is often required to include in light-sensitive photographic material one or more coloured layers. The object of these layers is to absorb unwanted light either by acting as filter layers which selectively absorb light of certain wave lengths and allow the remaining light to pass or to act as anti-halation layers. Anti-halation layers act by absorbing all the light which reaches them and thus prevent the light being reflected back into superposed light-sensitive layers. However once the light-sensitive material has been exposed it is required that the coloured layers be decolourised before or during the processing of the image so that the colour of the image is not distorted.
Such coloured layers often comprise a dye attached to a mordant compound the combination of dye and mordant being present in a binder layer which is very often gelatin. The coloured layer can be decolourised by removing the coloured layer entirely and this is often done when the coloured layer is an anti-halation backing layer. However filter layers are usually placed between image layers and thus cannot be removed without removing the superposed image layer. Further it is becoming a common practice in photosensitive materials, and in particular microfilm, to have an anti-halation under-layer, which layer is coated on the photobase under the image producing layer or layers. In such circumstance also it is impossible to remove the coloured layer. Thus there are left the possibilities of decolourising the coloured layer by removing the combination of dye plus mordant from the layer, rendering the dye colourless by chemical reaction or freeing the dye from the mordant by chemical reaction. The first of these alternatives has been found to be quite impractical because it is required that the mordant be substantive to the binder of the layer in order to obtain a uniform coloured layer during coating of the layer. The second alternative has been practised and to some extent is still practised; in fact sulphite which is a constituent of most developing solutions will bleach most of the anionic dyes used in coloured layers in photographic materials. However this bleaching action is slow and often incomplete and furthermore an undesirable yellow stain often results. Thus increasing attention has been paid to the third alternative and a number of mordant plus releasable dye combinations have been proposed. Most of these combinations employ so-called alkali-release mordants. When layers containing the combination of an anionic dye and an alkali-release mordant are treated with an alkaline solution the dye is released. The requirements for a suitable alkali-release mordant are:
(1) the anionic dye must be firmly bound to the mordant under all conditions except when the layer containing the mordant is treated with an alkaline solution,
(2) when the layer containing the anionic dye plus mordant combination is treated with an alkaline solution the dye must be released completely and rapidly from the mordant,
(3) the mordant and the mordant-dye combination must be resistant to diffusion in or from the binder of the layer in which the mordant is present,
(4) the mordant must be water-dispersible and compatible with the binder of the layer which is often gelatin.
When the alkali-release mordant is to be used in a layer in photographic material there are two other requirements:
(5) the mordant must not affect to any great extent the photographic properties of the photographic layer or layers with which it is adjacent,
(6) the mordant must not take up and retain the silver halide fixing agent used in the processing of the photographic material because such retention yields, on prolonged storage, a brown stain.